Atherosclerosis is a complex, progressive and degenerative condition resulting in the build-up of cholesterol and other occlusive materials, known as plaque, on the walls of blood vessels. The accumulation of plaque narrows the interior (lumen) of the vessels reducing blood flow. Plaque occurs in blood vessels in several different forms and can be located in many different anatomies throughout a vascular system. For example, an occluded vessel may lie in the blood vessels of the heart (coronary arteries) or in the peripheral vasculature supplying the extremities or other vital organ systems. Plaque can vary in composition, with portions that are hard and fibrous, known as calcified plaque, and other portions that are soft and fatty.
Over time, plaque deposits can become large enough to substantially reduce or totally occlude blood flow through a vessel, which can lead to symptoms associated with low blood flow, including cardiac arrest, stroke, or tissue or organ necrosis. Chronic total occlusions (CTOs) are one type of plaque deposit, usually including calcified plaque portions, which block the blood path through the affected vessel. To treat plaque deposits and improve or resolve low blood flow symptoms, it is desirable to restore or improve blood flow through the affected vessel.
Chronic total occlusions have historically been treated by performing a bypass procedure, where an autologous or synthetic blood vessel is anastomotically attached to locations on the native vessel upstream and downstream of the occlusion. While effective, such bypass procedures are quite traumatic to the patient and can become blocked over time. A more recent procedure for treating CTOs and other severe occlusions is percutaneous transluminal coronary angioplasty (PTCA). During a PTCA procedure, a small incision is (typically) made in the groin. A guide catheter is introduced into the femoral artery over a guidewire and advanced toward the occlusion. This is called an antegrade approach. A number of devices have been developed or used for the percutaneous interventional treatment of CTOs, such as stiffer guidewires, atherectomy devices, drills, drug eluting stents, and re-entry catheters.
A factor that is determinative of whether a treating clinician can successfully revascularize a CTO is the clinician's ability to advance a suitable guidewire from a position within the true lumen of a vessel proximal to the occlusion, across the CTO occlusion (i.e., either through the occlusion or around it), and then back into the true lumen of the vessel at a location distal to the occlusion. Once the guidewire is maneuvered into place by being passed into and across the occlusion, it can act as a rail for positioning a subsequent treatment device, such as a balloon-tipped angioplasty catheter. When appropriately positioned within the occlusion, the balloon can be inflated to apply radial pressure and compress the plaque deposit to increase blood flow through the affected vessel. Commonly, a stent is subsequently placed.